| 摘要 |
PURPOSE:To identify the image areas of a character, a line drawing, a photograph and a dotted photograph in image data and judging the picture hue of a noticed picture element based on results obtained by comparing the difference between the average density value of a block and the density value of the noticed picture element, the low and the high frequency components of a special frequency in the block with first, second and third thresholds, respectively. CONSTITUTION:Image data whose gradation is corrected by a gradation correction circuit 3 is inputted to a block making circuit 13 and a picture element in the prescribed size is segmented. A density difference detection circuit 7 takes the absolute value of the difference between the average density value and the density value of the noticed picture element. If the absolute value is smaller than a first threshold, the noticed picture element is decided to be in a halftone image area or in a background area, otherwise, it it decided to be in the image area of which density partly and violently changes. A space filter circuit 8 detects the image edge of a comparatively low frequency and compares it with a second threshold. If the edge is bigger, it is decided that a low frequency edge exists. A space filter 9 compares the image edge with a third threshold, and if the edge is bigger, it is decided that there is a high frequency edge including the dot. Based on these results, a decision circuit 10 identifies the image data on an original in which the photograph area, the character area and the dotted photograph area mixedly exist. |
